hdu 1455 sticks

经典剪枝题目，注释的别人代码。还是得自己多敲。反思，反思！

 1 #include "iostream"
 2 #include "algorithm"
 3 #include "memory.h"
 4 using namespace std;
 5
 6 int sticks[64],n,len,num;
 7 bool used[64];
 8
 9 bool cmp(int a,int b)
10 {
11     return a > b;
12 }
13
14 bool dfs(int cur,int left,int level)
15 {  //cur: 当前已经计算的木棒编号，left:该段还剩的长度，level:已经成功的木棒数
16     if (left == 0) {//匹配一根木棒成功
17         if (level == num-2)  return true;
18         for (cur = 0; used[cur];cur++);//找到下一个未访问过的长度
19         used[cur] = true;
20         if (dfs(cur+1,len-sticks[cur],level+1))
21             return true;
22         used[cur] = false;              //回溯
23         return false;
24     } else {
25             if (cur >= n-1) return false;
26             for (int i = cur;i < n; ++ i) {//剪枝
27                 if (used[i]) continue;      //访问过的长度
28                 if (sticks[i] == sticks[i-1] && !used[i-1]) continue; //相等的长度已经搜过的不搜
29                 if (sticks[i] > left) continue;                     //大于达到len的生育长度
30                 used[i] = true;
31                 if (dfs(i,left-sticks[i],level)) return true;
32                 used[i] = false;        //回溯
33             }
34         return false;
35     }
36 }
37 int main()
38 {
39     while (cin >> n,n) {
40         int sum = 0;
41         for (int i = 0;i < n; ++ i) {
42             cin >> sticks[i];
43             if(sticks[i]>50)
44             {
45                 n--;i--;continue;
46             }
47             sum += sticks[i];
48         }
49         sort(sticks,sticks + n,cmp);//剪枝
50         bool end = false ;
51         for (len = sticks[0]; len <= sum/2; len++) {
52             if (sum%len == 0) {     //剪枝
53                 used[0] = true;
54                 num = sum/len;
55                 if (dfs(0,len-sticks[0],0)) {
56                     end = true;
57                     cout << len << endl;
58                     break;
59                 }
60                 used[0] = false;    //回溯
61             }
62         }
63         if (!end) cout << sum << endl;
64         memset(used,0,sizeof(used));
65     }
66     return 0;
67 }